1. Field of the Invention
The invention relates to sealing means such as packing and tip seals for the diaphragm and other stationary parts of an elastic fluid axial flow turbine. Such sealing means are arranged both where rotatable shafts penetrate stationary turbine casings and in addition, internal to the casings between stages and turbine sections. The sealing means prevent or reduce leakage of the fluid by creating small clearance areas with low flow coefficients between the rotating and stationary parts.
A typical steam turbine diaphragm consists of the shaft packing, nozzles, and spill strips or tip seals. Historical data collected has indicated that in most units inspected, the radial spill strips were rubbed approximately 50% more than the shaft packing. The spill strip design essentially holds the seal rigidly in place, whereas the shaft packing are spring-backed, allowing the packing ring segments to back away from the shaft to some degree.
Reductions in steam turbine efficiency and performance are primarily caused by four mechanisms:
1. Chemical deposits in the turbine steam path; PA0 2. Erosion on nozzle and bucket surfaces; PA0 3. Mechanical damage to nozzles and buckets from foreign material; and PA0 4. Steam leakage through shaft packing rings and tip seals.
Assuming proper alignment of the diaphragms and rotor, packing and tip seal rubs are usually the result of thermal distortion. Thermal distortion is most prevalent during transient operating conditions, such as turbine start-up.
Leakage problems are presented by out of round diaphragms or misaligned rotors.
2. Description of the Prior Art
The packing and tip seals of the prior art are unsuitable for use with turbines having out of round diaphragms or misaligned rotors.
To my knowledge, all of the packing or tip seals are of rigid one piece construction so as not to provide suitable sealing means when turbine parts are not true, are out of round, or are misaligned.
SUMMARY OF THE INVENTION
It is a primary object of the invention to provide sealing means such as two part packing rings and tip seals each comprising separate half parts and means for selectively varying the spacing between the half parts for adjusting the sealing dimensions of the packing and tip seals.
The means for selectively varying the spacing between the half parts may be a shim or shims, or adjusting screws on one half part bearing against hardened steel pads on the other half part.